Biological Sensing Structures

ABSTRACT

A biological sensing structure includes a mesa integrally connected a portion of a substrate, wherein the mesa has a top surface and a sidewall surface adjacent to the top surface. The biological sensing structure includes a first light reflecting layer over the top surface and the sidewall surface of the mesa. The biological sensing structure includes a filling material surrounding the mesa, wherein the mesa protrudes from the filling material. The biological sensing structure includes a stop layer over the filling material and a portion of the first light reflecting layer. The biological sensing structure includes a second light reflecting layer over a portion of the stop layer and a portion of the top surface of the mesa. The biological sensing structure includes an opening in the second light reflecting layer to partially expose the top surface of the mesa.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/491,255, filed on Sep. 19, 2014, and entitled “Biological SensingStructures,” which is a divisional of U.S. application Ser. No.13/372,141, filed Feb. 13, 2012, now U.S. Pat. No. 8,846,129, issued onSep. 30, 2014, and entitled “Biological Sensing Structures and Methodsof Forming the Same,” which applications are incorporated herein byreference in their entireties.

TECHNICAL FIELD

This disclosure relates to biological sensing structures.

BACKGROUND

Biological sensing structures or Biosensors are devices for sensing anddetecting biomolecules and operate on the basis of electronic or opticaldetection principles. An advantage of biological sensing structures isthe prospect of label-free operation. Specially, biological sensingstructures enable the avoidance of costly and time-consuming labelingoperations such as the labeling of an analyte with, for example,fluorescent or radioactive agents.

Biological sensing structures or biosensors can be manufactured usingsemiconductor processes. Biological sensing structures can quicklydetect electrical or optical signals and can be easily applied tointegrated circuits (ICs) and micro electro mechanical systems (MEMS).Despite the attractive properties noted above, a number of challengesexist in connection with developing biosensors. Various techniquesdirected at configurations and methods of forming these biosensors havebeen implemented to try and further improve device performances.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure may be understood from the followingdetailed description and the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a top view of a wafer including a plurality of biologicalchips on a substrate according to one or more embodiments of thisdisclosure.

FIG. 1B is an enlarged view of a single biological chip of FIG. 1Aaccording to one or more embodiments of this disclosure.

FIG. 2 is a flowchart of a method of forming a structure of a biologicalchip having a biological sensing structure according to one or moreembodiments of this disclosure.

FIG. 3A is a top view of a structure of the single biological chip ofFIG. 1B according to one or more embodiments of this disclosure.

FIG. 3B is a perspective view of the single biological chip along lineA-A′ in FIG. 3A according to one or more embodiments of this disclosure.

FIGS. 4 to 11B are cross-sectional views of the structure of thebiological chip having a biological sensing structure at various stagesof manufacture according to various embodiments of the method of FIG. 2.

FIG. 12 is a top view of the single biological chip of FIG. 1B having aplurality of biological sensing structures formed in an arrangement ofan array.

FIG. 13 illustrates an enlarged cross-sectional view of a biologicalsensing structure in an operation of detecting biomolecules.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific examples of components are arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the formation of a first feature over or on a second feature in thedescription that follows may include embodiments in which the first andsecond features are formed in direct contact, and may also includeembodiment in which additional features may be formed interposing thefirst and second features, such that the first and second features maynot be in direct contact. Further still, references to relative termssuch as “top”, “front”, “bottom”, and “back” are used to provide arelative relationship between elements and are not intended to imply anyabsolute direction. Various features may be arbitrarily drawn indifferent scales for simplicity and clarity.

FIG. 1A is a top view of a wafer 100 including a plurality of biologicalchips 103 marked on a substrate 102. The plurality of biological chips103 are divided by scribe lines 106 between the biological chips 103.FIG. 1B is an enlarged view of a single biological chip 103 depicted inFigure IA. The substrate 102 will go through a variety of cleaning,layering, patterning, etching or doping steps to form biological sensingstructures in the biological chips 104. The term “substrate” hereingenerally refers to a bulk substrate that is suitable for transmittingelectrical or optical signals of an analyte. In at least one example,the substrate includes a transparent material, such as quartz, sapphire,fused silica or other suitable glasses. In another example, thesubstrate is a rigid material which keeps the observed analyte in fixedpositions during observation. In yet another example, the substrate is atransparent organic material, for example, methacrylate polymers such asPMMA, polycarbonates, cyclic olefin polymers, styrenic polymers,fluorine-containing polymers, polyesters, polyetherketones,polyethersulfones, polyimides or mixtures thereof. In some embodiments,vanous layers and devices structures are formed over the substrate.Examples of such layers include dielectric layers, doped layers,polysilicon layers or conductive layers. Examples of device structuresinclude transistors, resistors, and/or capacitors, which may beinterconnected through an interconnect layer to additional devices.

FIG. 2 is a flowchart of a method 200 of forming a structure of abiological chip having a biological sensing structure according to oneor more embodiments of this disclosure. The method 200 may includeforming the biological sensing structure using one or more process stepscompatible with a complementary metal-oxide-semiconductor (CMOS)process. It is understood that the method 200 includes steps havingfeatures of a typical CMOS technology process flow and thus, are onlydescribed briefly herein. Further, it is understood that additionalsteps can be provided before, during, and after the method 200. Some ofthe steps described below can be replaced or eliminated for additionalembodiments of the method 200. FIGS. 4 to 11 are cross-sectional viewsof a structure 104 of a biological chip having a biological sensingstructure at various stages of manufacture according to variousembodiments of the method 200 of FIG. 2. Various figures have beensimplified for a better understanding of the inventive concepts of thepresent disclosure.

Referring to FIGS. 2 and 4, the method 200 begins with operation 201 inwhich a portion of a substrate is recessed to form a plurality of mesas.The recess operation may be formed by using suitable photolithographyprocess to provide a pattern on the substrate. Then, etching processesare performed to remove a portion of the substrate to define theplurality of mesas. The adjacent mesas are separated by a recess. Theetching processes may include wet etch, dry etch, plasma etch and/orother suitable processes.

Referring the example of FIG. 4, a portion of a substrate 102 isrecessed to form a plurality of mesas 108. The recessed portion of thesubstrate 102 forms a plurality of recesses 110 surrounding each mesa108. The adjacent mesas 108 are separated by a recess 110. In oneembodiment, the mesas 108 are in an arrangement of an array as shown inFIG. 3A with a top view of the structure 104 of the biological chip.FIG. 3B is a perspective view of the mesas 108 along line A-A′ in FIG.3A. FIG. 4 is the cross-sectional view of the mesas 108 along line A-A′in FIG. 3A. The substrate 102 has a top surface 102A and a bottomsurface 102B. The recesses 110 extend from the top surface 102A into thesubstrate 102 with a depth D of about 6 μm to 7 μm, while notpenetrating through the bottom surface 102B. The recess 110 has aninterior surface 110A and a bottom surface 110B. The mesa 108 has a topsurface and a sidewall surface adjacent to the top surface. The topsurface of the mesa 108 is the same as the top surface 102A of thesubstrate 102. The sidewall surface of the mesa 108 is the same as theinterior surface 110A of the recess 110. In one example, the mesa 108has an interior angle, Angle 1, between a plane parallel to the bottomsurface 110B and the interior surface 110A, from about 60° to about 85°.In another example, the mesa 108 has the interior angle, Angle 1, fromabout 75° to about 85°.

Referring to FIGS. 2 and 5, the method 200 continues with operation 202in which a first light reflecting layer is deposited over the substrateto cover each mesa. The first light reflecting layer includes a metallicmaterial such as aluminum, copper, gold, silver, chrome, or mixturesthereof. The first light reflecting layer may be formed by a suitableprocess, such as physical vapor deposition (PVD), chemical vapordeposition (CVD) or atomic layer deposition (ALD). The first lightreflecting layer can also comprise a reflective organic polymer, such asa composite material comprising reflective particles dispersed in apolymeric material.

Referring the example of FIG. 5, a first light reflecting layer 112 isdeposited over the substrate102 to cover the top surface 102A and theinterior surface 110A of each recess 110, and the bottom surface 110B ofthe recesses 110. In one example, the first light reflecting layer 112has a thickness ranging from about 1000 Å to about 3000 Å. The mesa 108and the first light reflecting layer 112 disposed on an outside surface(102A and 110A) of the mesa 108 is configured as a micro-mirror. Thefirst light reflecting layer 112 may enhance the reflectivity of theoutside surface (102A and 110A) of the mesa 108. The operation of themicro-mirror will be explained further in the later section as shown inFIG. 13.

Referring to FIGS. 2 and 6, the method 200 continues with operation 203in which a filling material is formed over a first portion of the firstlight reflecting layer to expose a second portion of the first lightreflecting layer. In some embodiments, the filling material includessilicon oxide, low k dielectric material or other suitable dielectricmaterials. The filling material is formed by low temperature chemicalvapor deposition (LTCVD) at an operation temperature less than 300° C.to prevent damaging the substrate for electrical or optical signalsdetection. In at least another embodiment, the filling material mayinclude PMMA, polycarbonates, cyclic olefin polymers, styrenic polymers,fluorine-containing polymers, polyesters, polyetherketones,polyethersulfones, polyimides or mixtures thereof deposited by spincoating.

In at least one embodiment, the filling material is formed on thesubstrate to a level above top surfaces of the mesas and the first lightreflecting layer. A planarization process, such as a chemical mechanicalpolishing (CMP) process and/or an etching process, is applied to thefilling material to reduce the thickness of the filling material toexpose the second portion of the first light reflecting layer. In oneembodiment, the planarized filling material partially fills each recessbetween adjacent mesas and leaves remaining recesses. The planarizedfilling material has a top surface lower than the top surface of eachmesa. The second portion of the first light reflecting layer on eachmesa protrudes from the top surface of the surrounding filling material.Each remaining recess has a depth W between the top surface of each mesaand the top surface of the planarized filling material.

Referring the example of FIG. 6, a filling material 114 partially fillsthe recesses 110 surrounding each mesa 108 and leaves remaining recesses110C. The filling material 114 has a top surface 114A lower than the topsurface 102A of each mesa 108. A first portion 112A of the first lightreflecting layer 112 is embedded in the filling material 114. A secondportion 112B of the first light reflecting layer 112 on the top surface102A of the mesa 108 and a top portion of the sidewall surface 110A ofthe mesa 108 is exposed from the filling material 114. A depth W of theremaining recess 110C is less than about 6000 A.

Referring to FIGS. 2 and 7, the method 200 continues with operation 204in which a stop layer is deposited over the filling material and thesecond portion of the first light reflecting layer. In some embodiments,the stop layer includes silicon oxide, silicon nitride, siliconoxy-nitride or other suitable materials which have higher etching orpolishing resistance compared to a following formed sacrificial layer.In some examples, the stop layer is a conformal liner along the topsurface of the filing material and the second portion of the first lightreflecting layer. The stop layer has a thickness T less than the depth Wof the remaining recesses. The stop layer may be formed by plasmaenhanced chemical vapor deposition (PECVD), high aspect ratio process(HARP), ALD or a spin on dielectric (SOD).

Referring the example of FIG. 7, a stop layer 116 is deposited over thefilling material 114 and the second portion 112B of the first lightreflecting layer 112. In some embodiments, the stop layer 116 is aconformal liner along the top surface 114A of the filing material 114and the second portion 112B of the first light reflecting layer 112, anddoes not overfill the remaining recesses 110C. The stop layer 116 has athickness T less than the depth W of the remaining recesses 110C. Thethickness T is in a range of about 1000 A to about 2500 A. A ratio ofthe depth W to the thickness T is larger than about 5. The stop layer116 may include silicon oxide, silicon nitride, silicon oxy-nitride, orother suitable materials which have higher etching or polishingresistance compared to a following formed sacrificial layer 118.

Referring back to FIG. 2, the method 200 continues with operation 205 inwhich the sacrificial layer is formed over the stop layer to a levelabove a top surface of the stop layer over the mesas. Namely, thesacrificial layer overfills the remaining recesses. In one embodiment,the sacrificial layer includes polycrystalline silicon, amorphoussilicon or other suitable materials which have less etching or polishingresistance compared to the stop layer formed in operation 204. Thesacrificial layer may be formed by CVD, PECVD or low pressure chemicalvapor deposition (LPCVD).

Referring to FIGS. 2 and 8, the method 200 continues with operation 206in which the sacrificial layer is planarized to expose a portion of thestop layer. A planarization operation, such as a chemical mechanicalpolishing (CMP) process and/or an etching process, is applied to thesacrificial layer to reduce the thickness of the sacrificial layer toexpose a portion of the stop layer. In some embodiments, the processconditions and parameters of the CMP process, including slurry chemicaland polishing pressure, are tuned to planarize the sacrificial layer.The stop layer has higher etching or polishing resistance compared tothe sacrificial layer in operation 206. The planarization operation 206could cease as the top surface of the stop layer is exposed. In at leastone example, a removed rate ratio of the sacrificial layer to the stoplayer is larger than about 100. In at least another example, the removedrate ratio of the sacrificial layer to the stop layer is larger thanabout 400. In some embodiments, a top surface of the planarizedsacrificial layer and the top surface of the stop layer over the mesashave a step height less than 3000 Å. In at least another embodiment, thetop surface of the planarized sacrificial layer is substantially planarto the top surface of the stop layer over the mesas. Advantageously, useof the stop layer improves the uniformity of the planarized surface ofthe sacrificial layer. The planarized sacrificial layer and the topsurface of the stop layer over the mesas get a smooth new surface. Thesmooth new surface would achieve a better resolution for the followinglithography process on the new surface. The device performance and yieldon the completed products are thus significantly increased.

Referring the example of FIG. 8, the structure 104 of the biologicalchip illustrates a cross-sectional view after performance of operations205 and 206. A sacrificial layer 118 is formed over the stop layer 116and planarized. A portion of the stop layer 116 over each mesa 108 isexposed. In some embodiments, a top surface of the planarizedsacrificial layer and the top surface of the stop layer over the mesashave a step height (not shown) less than 3000 A. In another embodiment,the top surface of the planarized sacrificial layer 118 is substantiallyplanar to the top surface of the stop layer 116 over the mesas 108.

Referring to FIGS. 2 and 9A, the method 200 continues with operation 207in which a first opening is formed in the stop layer and the secondportion of the first light reflecting layer to partially expose a topsurface of each mesas. The first opening forming operation may be formedby using suitable photolithography process to provide a pattern on thestop layer. The patterned stop layer is then subjected to etchingprocesses to remove a portion of the stop layer and the first lightreflecting layer to define the first opening.

Referring the example of FIG. 9A, a first opening 120 is formed in thestop layer 116 and the second portion 112B of the first light reflectinglayer 112 to expose a portion of the top surface 102A of each mesa 108.FIG. 9B illustrates an enlarged cross-sectional view of a portion of thestructure 104 of the biological chip in FIG. 9A. In at least oneexample, the first opening 120 has a width W1 and an interior angle,Angle 2, between the top surface 102A and a tapered sidewall 120A,greater than 90°. In at least another example, the interior angle, Angle2, is greater than about 100°. In some embodiments, the first lightreflecting layer 112 is aluminum. The aluminum layer is etched with aplasma process in a BCl₃/Cl₂ ambient environment. A gas ratio ofBCl₃/Cl₂ is in a range from about 0.5 to about 1.3. Within this gasratio, the first opening 120 has the tapered sidewall 120A with theinterior angle, Angle 2, greater than 90°.

Referring to FIGS. 2 and 10A, the method 200 continues with operation208 in which a second light reflecting layer is deposited over the firstopening and the partially exposed top surface of each mesa. The secondlight reflecting layer is an opaque or reflective material. The secondlight reflecting layer may be compatible (e.g., friendly) for bio-entitybinding. In some embodiments, the second light reflecting layer includesa metallic material such as aluminum, copper, gold, silver, chromium,titanium or mixtures thereof. The second light reflecting layer may beformed by a suitable process, such as physical vapor deposition (PVD),CVD or atomic layer deposition (ALD).

Referring the example of FIG. 10A, a second light reflecting layer 122is deposited over the structure 104 of the biological chip in FIG. 9A.The second light reflecting layer 122 conformally covers the planarizedsacrificial layer 118, the tapered sidewall 120A of the first openings120 and the exposed portion of the top surface 102A of each mesa 108.FIG. 10B illustrates an enlarged cross-sectional view of a portion ofthe structure 104 of the biological chip in FIG. 10A. In at least oneexample, the second light reflecting layer 122 has a thickness fromabout 700 Å to about 1600 Å. Advantageously, the tapered sidewall 120Aof the first opening 120 improves the step coverage of the followingsecond light reflecting layer 122 deposition, prevents the second lightreflecting layer 122 tends to overhang at the top corner of the firstopening 120 and reduces the chance to seal the first opening 120prematurely with a void formed under the overhang.

Referring to FIGS. 2 and 11A, the method 200 continues with operation209 in which a second opening is formed in the second light reflectinglayer to partially expose the top surface of each mesa. The secondopening forming operation may be formed by using a suitablephotolithography process and etching processes to remove a portion ofthe second light reflecting layer to define a second opening.

Referring the example of FIG. 11A, a second opening 124 in formed in thesecond light reflecting layer 122 to partially expose the top surface102A of each mesa 108. FIG. 11B illustrates an enlarged cross-sectionalview of a portion of the structure 104 of the biological chip in FIG.11A. As shown in FIG. 11B, the second opening 124 has a tapered sidewall124A with an interior angle, Angle 3, between the top surface 102A andthe tapered sidewall 124A, in a range from about 90° to about 145°. Insome embodiments, the second light reflecting layer 122 is aluminum. Thealuminum layer is etched with a plasma process in a BC1 ₃/C1 ₂ ambientenvironment. A gas ratio of BCl₃/Cl₂ is in a range of about 0.5 to about1.3 for the tapered sidewall 124A. The second opening 124 is capable ofcontaining an observed analyte. The analyte may include an enzyme, anantibody, a ligand, a peptide, an oligonucleotide, a cell of an organ,an organism or a piece of tissue. In at least one example, the secondopening 124 has a width W₂ less than the width W₁ of the first opening120. In at least another example, the width W₂ of the second opening 124larger than the width W₁ of the first opening 120. In at least anotherexample, the width W₂ of the second opening 124 is in a range from about120 nm to about 160 nm. In at least another example, the width W₂ of thesecond opening 124 is capable of containing only one molecule of theanalyte. The width W₂ contains a single DNA (deoxyribonucleic acid)polymerase within the second opening 124. After the operation 209, abiological sensing structure 125 having a micro-mirror is formed in thestructure 104 of biological chip. In one embodiment, a plurality ofbiological sensing structures 125 are formed in an arrangement of anarray on the structure 104 of the biological chip as shown in FIG. 12. Aportion of the top surface 102A of each mesa 108 is exposed by thesecond opening 124 while other portions of the structure 104 of thebiological chip covered by the second light reflecting layer 122.

In some embodiments, further process steps are optionally included afterthe operation 209. In some embodiments, a mechanically sawing or a lasersawing is performed along the scribe lines 106 of the wafer 100 and thesubstrate 102 are sawed into individual biological chips 103.

FIG. 13 illustrates an enlarged cross-sectional view of a biologicalsensing structure 125 in an operation of detecting biomolecules. Thebiological sensing structure 125 includes a mesa 108 integrallyconnected a portion of a substrate 102. The mesa 108 has the top surface102A and the sidewall surface 110A adjacent to the top surface 102A. Afirst light reflecting layer 112 is disposed over the top surface 102Aand the sidewall surface 110A of the mesa 108. The mesa 108 and thefirst light reflecting layer 112 disposed on the outside surface (102Aand 110A) of the mesa 108 is configured as a micro-mirror. A fillingmaterial 114 surrounds the mesa 108. The mesa 108 protrudes from a topsurface 114A of the filling material 114. The stop layer 116 is disposedover the filling material 114 and the second portion of the firstreflecting layer 112. The sacrificial layer 118 is disposed over thefirst portion of the stop layer 116 and exposes the second portion ofthe stop layer 116. The second light reflecting layer 122 is disposedover the second portion of the stop layer 116 and a portion of the topsurface 102A of the mesa 108. The opening 124 is disposed in the secondlight reflecting layer 122 to partially expose the portion of the topsurface 102A of the mesa 108. During the detecting operation, an analyte126 is disposed in the second opening 124 of the biological sensingstructure 125. The analyte 126 may include an enzyme, an antibody, aligand, a peptide, an oligonucleotide, a cell of an organ, an organismor piece of tissue. A source of excitation radiation (not shown)generates radiation incident on the analyte 126. The analyte 126 mayemit a light output 128 to the underneath micro-mirror. The micro-mirrorreflects the light output 128 and conveys the light output 128 to adetector 127 below the bottom surface 102B of substrate 102. Thedetector 127 collects the light output 128 and stores the light output128 in a storage apparatus for analysis. The first light reflectinglayer 112 may enhance the reflectivity of the outside surface (102A and110A) of the mesa 108. The second opening 124 in the second lightreflecting layer 122 confines the analyte 126 within the opening 124.The second light reflecting layer 122 on the top surface 102A of themesa 108 also reflects the light output 128 to the detector 127.

Various embodiments of the present disclosure may be used to improve theperformance of a biological chip having a biological sensing structure.For example, the stop layer 116 improves the uniformity of theplanarized surface of the sacrificial layer 118. The planarizedsacrificial layer 118 and the top surface of the stop layer 116 over themesas 108 form the smooth new surface. The smooth new surface enhancescapability to achieve a better resolution of the following lithographyprocess on the new surface. The tapered sidewall 120A of the firstopening 120 improves the step coverage of the following second lightreflecting layer 122 deposition and prevents the second light reflectinglayer 122 from overhanging at the top corner of the first opening 120.Due to the better resolution of the lithography process in defining thepatterns of the second openings 124, the dimension of the secondopenings 124 among the biological chips 104 on the same wafer 100 couldbe accurately controlled during the etching process. The electrical oroptical performances of each biological sensing structure 125 in thesame biological chip 104 or the same wafer 100 could be tightly binned.

One aspect of this description relates to a biological sensingstructure. The biological sensing structure includes a mesa integrallyconnected a portion of a substrate, wherein the mesa has a top surfaceand a sidewall surface adjacent to the top surface. The biologicalsensing structure further includes a first light reflecting layerdisposed over the top surface and the sidewall surface of the mesa. Thebiological sensing structure further includes a filling materialsurrounding the mesa, wherein the mesa protrudes from a top surface ofthe filling material. The biological sensing structure further includesa stop layer disposed over the filling material and a portion of thefirst light reflecting layer. The biological sensing structure furtherincludes a sacrificial layer disposed over a first portion of the stoplayer and exposing a second portion of the stop layer. The biologicalsensing structure further includes a second light reflecting layerdisposed over the second portion of the stop layer and a portion of thetop surface of the mesa. The biological sensing structure furtherincludes an opening disposed in the second light reflecting layer topartially expose the top surface of the mesa.

Another aspect of this description relates to a biological sensingarray. The biological sensing array includes a plurality of mesas in asubstrate, wherein each of the plurality of mesas has a top surface anda sidewall surface adjacent to the top surface. The biological sensingarray further includes a first light reflecting layer covering the topsurface and the sidewall surface of each mesa of the plurality of mesas.The biological sensing array further includes a filling materialsurrounding each mesa, wherein the filling material exposes a portion ofthe first light reflecting layer, and each mesa of the plurality ofmesas protrudes from a top surface of the filling material by a stepheight W. The biological sensing array further includes a stop layerover the filling material and the exposed portion of the first lightreflecting layer, wherein the stop layer has a thickness T less than thestep height W. The biological sensing array further includes asacrificial layer over the stop layer, wherein the sacrificial layerpartially exposes the stop layer. The biological sensing array furtherincludes a first opening in the stop layer and the first lightreflecting layer, the first opening partially exposing the top surfaceof each mesa of the plurality of mesas, and the first opening includes awidth W₁. The biological sensing array further includes a second lightreflecting layer over at least the first opening and the partiallyexposed top surface of each mesa. The biological sensing array furtherincludes a second opening in the second light reflecting layer topartially expose the top surface of each mesa, wherein the secondopening includes a width W₂ less than the width W₁.

Still another aspect of this description relates to a biological sensingstructure. The biological sensing structure includes a mesa in asubstrate; and a first light reflecting layer covering a top surface andsidewall surface of the mesa. The biological sensing structure furtherincludes a filling material over a first portion of the first lightreflecting layer, wherein the filling material exposes a second portionof the first light reflecting layer. The biological sensing structurefurther includes a first opening in the first light reflecting layer,wherein the first opening exposes a first portion of the top surface ofthe mesa. The biological sensing structure further includes a secondlight reflecting layer over the first opening, wherein the second lightreflecting layer exposes a portion of the top surface of the mesa. Thebiological sensing structure further includes a second opening in thesecond light reflecting layer, wherein the second opening exposes asecond portion of the top surface of the mesa.

An aspect of this description relates to a biological sensor including asubstrate and a mesa extending from the substrate and being formed ofthe same material as the substrate. The sensor further includes a firstlight reflecting layer conformally overlying the mesa, the first lightreflecting layer having a first opening therethrough exposing a firstregion of the mesa and a second light reflecting layer conformallyoverlying a portion of the first light reflecting layer, the secondlight reflecting layer extending into the first opening, the secondlight reflecting layer having a second opening therethrough exposing asecond region of the mesa, the second region overlapping the firstregion.

In another aspect of this description, a biological sensing structure isprovided. The structure includes a mesa in a substrate, a first lightreflecting layer over a top surface and sidewall surface of the mesa, afirst opening in the first light reflecting layer, wherein the firstopening exposes a first portion of the top surface of the mesa, a secondlight reflecting layer over the first light reflecting layer and in thefirst opening, and a second opening in the second light reflectinglayer, wherein the second opening exposes a second portion of the topsurface of the mesa.

In a further aspect of this description, a biological sensing structureincludes at least two recesses in a substrate leaving a mesatherebetween. The structure further includes a first light reflectinglayer over a top surface and sidewalls of the mesa and over a bottomsurface of the at least two recesses, a first opening in the first lightreflecting layer, the first opening exposing a portion of the topsurface of the mesa, and the first opening having a tapered sidewall, asecond light reflecting layer over the first light reflecting layer, onthe tapered sidewalls of the first opening, and in the first opening,and a second opening in the second light reflecting layer, wherein thesecond opening at least partially exposes the portion of the top surfaceof the mesa.

Although the embodiments and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods, and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A biological sensor, comprising: a substrate; amesa extending from the substrate and being formed of the same materialas the substrate; a first light reflecting layer conformally overlyingthe mesa, the first light reflecting layer having a first openingtherethrough exposing a first region of the mesa; and a second lightreflecting layer conformally overlying a portion of the first lightreflecting layer, the second light reflecting layer extending into thefirst opening, the second light reflecting layer having a second openingtherethrough exposing a second region of the mesa, the second regionoverlapping the first region.
 2. The biological sensor of claim 1,wherein the second opening is configured to receive an analyte.
 3. Thebiological sensor of claim 1, wherein sidewalls of the first opening aretapered and have an interior angle of greater than about 90°.
 4. Thebiological sensor of claim 1, wherein sidewalls of the second openingare tapered and have an interior angle in a range from about 90° toabout 145°.
 5. The biological sensor of claim 1, wherein the firstopening has a width W₁ and the second opening has a width W₂.
 6. Thebiological sensor of claim 5, wherein the width W₁ is greater than thewidth W₂.
 7. The biological sensor of claim 5, wherein the width W₁ issmaller than the width W₂.
 8. The biological sensor of claim 1, furthercomprising a detector underlying the substrate.
 9. A biological sensingstructure comprising: a mesa in a substrate; a first light reflectinglayer over a top surface and sidewall surface of the mesa; a firstopening in the first light reflecting layer, wherein the first openingexposes a first portion of the top surface of the mesa; a second lightreflecting layer over the first light reflecting layer and in the firstopening; and a second opening in the second light reflecting layer,wherein the second opening exposes a second portion of the top surfaceof the mesa.
 10. The biological sensing structure of claim 9, wherein aninside angle between the sidewall surface of the mesa and a plane of atop surface of the substrate ranges from 60° to 85° .
 11. The biologicalsensing structure of claim 9, further comprising a recess in thesubstrate adjacent the mesa, wherein the first light reflecting layerextends along a bottom surface of the recess.
 12. The biological sensingstructure of claim 11, further comprising a filling material, a stoplayer, and a sacrificial layer in the recess.
 13. The biological sensingstructure of claim 11, wherein the recess has a depth of about 6 μm toabout 7 μm.
 14. The biological sensing structure of claim 9, wherein thesecond portion of the top surface of the mesa at least partiallyoverlaps the first portion of the top surface of the mesa.
 15. Thebiological sensing structure of claim 9, wherein the first lightreflecting layer comprises a metallic material.
 16. A biological sensingstructure comprising: at least two recesses in a substrate leaving amesa therebetween; a first light reflecting layer over a top surface andsidewalls of the mesa and over a bottom surface of the at least tworecesses; a first opening in the first light reflecting layer, the firstopening exposing a portion of the top surface of the mesa, and the firstopening having a tapered sidewall; a second light reflecting layer overthe first light reflecting layer, on the tapered sidewalls of the firstopening, and in the first opening; and a second opening in the secondlight reflecting layer, wherein the second opening at least partiallyexposes the portion of the top surface of the mesa.
 17. The biologicalsensing structure of claim 16, wherein the second opening has a taperedsidewall, and wherein an interior angle between the top surface of themesa and the tapered sidewall of the second opening is in a rangebetween about 90° to about 145°.
 18. The biological sensing structure ofclaim 17, wherein an interior angle between the top surface of the mesaand the tapered sidewall of the first opening is greater than about 90°.19. The biological sensing structure of claim 16, further comprising adetector underlying the substrate.
 20. The biological sensing structureof claim 16, further comprising: a filling material over the first lightreflecting layer in the at least two recesses; a conformal liner layerover the first light reflecting layer in the at least two recesses; anda sacrificial material over the conformal liner layer in the at leasttwo recesses, wherein the second light reflecting layer is over thesacrificial material.